Have ready clean plastic or glass containers and lids.
Peel and pit peaches. Finely chop or pulse fruit in a food processor until diced. Measure exactly 3 cups of diced peaches into a large bowl (You can eat any extra diced peaches leftover after measuring 3 cups.)
Add one cup of sugar to the bowl and stir well. Rest for 5 minutes. Repeat with remaining sugar, adding it a little at a time and resting in between. Stir in lemon juice. Let mixture rest for 10 min.
Taste the mixture and if it's still grainy from the sugar don't proceed until the sugar has dissolved! (If needed, you could place the heat-proof bowl or peaches over a saucepan of warm water on the stove. Gently stir the mixture and the heat will help the sugar to dissolve.)
Meanwhile, add the water and pectin to a small saucepan and stir to combine. Bring mixture to a boil, stirring constantly. Boil and stir for 1 minute, then remove from heat and add to the peach mixture. Stir jam for 3 minutes.
You should notice the jam has thickened a little. A will continue to thicken a bit more as it rests. (See notes, if it is still very runny).
Fill your glass or plastic containers, leaving 1/2 inch headspace. Wipe rim of jars clean and cover with lids. Let stand at room temperature 24 hours. (This allows the jam time to set up, but feel free to enjoy one of the jars right away!)
Store jam in the refrigerator for up to 3 weeks or freeze for up to 1 year.
What to do if your Jam is still too soft or runny:
Some peaches are juicier than others, so if you have extra juicy peaches and your jam doesn't set up as much as you'd like, you can cook another package of pectin (step 4 of the recipe) and add half or all of the mixture, to thicken it further.Keep in mind it will set up more as it rests.